Medical treatments constantly change over time, and the changes are usually for the better. How does this happen? It is possible to study the history of therapeutic change to gain insight into the nature of innovation in medicine. This insight can contribute not just to a future of continuing innovation, but also to medical decision making today. On the Origins of Therapies will analyze the history of cardiac surgery, focusing on the treatments of coronary artery disease. In 1968 surgeons developed coronary artery bypass grafting, one of the most important operations of the twentieth century. Inspired by this example, cardiologists developed a related technique, coronary angioplasty. Doctors did not develop these techniques from scratch. Instead, over the preceding fifty years, they had made amazingly creative attempts to design surgical treatments for coronary artery disease, either by increasing the supply of blood to the heart or by reducing the heart's need for it. Patients and doctors believed that many of these techniques worked, even ones that surgeons would now dismiss. Understanding how and why this happened is a major challenge for the history of medicine, and one that sheds light on the faith we now have in therapies today. On the Origin of Therapies will be grounded in extensive research, including a thorough review of thousands of articles from the published medical literature and careful analyses of rich archival collections that survive at prominent medical centers in Boston, Montreal, Cleveland, and Houston. It will focus on three sets of questions. First, it will examine the interplay between surgical imagination and bodily constraint, mapping the sources of creativity and innovation in surgical practice, as well as the limits of what could safely be done to bodily tissues. Second, it will explore the tensions that exist among different modes of assessing therapeutic efficacy, for instance how surgeons weighed the relative value of restored blood flow, decreased angina, and prolonged survival. Third, it will probe the impact of the pervasive rhetoric of progressive therapeutic evolution in the medical literature: faith in ongoing and inevitable progress gave surgeons the confidence to test daring techniques and a justification for downplaying the dictates of evidence based medicine. On the Origins of Therapies will be a major contribution to the literature on the history of medicine and will be essential reading for anyone interested in th processes of therapeutic change.